Polarizing plates are used inside and outside a liquid crystal cell for purpose of controlling an oscillation direction of light in order to visualize display patterns of a liquid crystal display apparatus. The polarizing plate includes a polarizer, and a protective film, which is formed on at least one side of the polarizer. Typically, although the protective film is a triacetyl cellulose (TAC) film, the TAC film is more expensive than typical polymer films. Therefore, low-priced polymer films including polyethylene terephthalate (PET) films are used to replace the TAC film.
A common PET film is a film which is drawn in a machine direction (md) and/or a transverse direction (td) by a certain draw ratio in order to improve a yield and have a range of phase difference (i.e., retardation). However, the common pet film which is drawn in md and td has high molecular orientation angle, and thus there is a large deviation between an absorption axis of a polarizer and an optical axis of the pet film. Therefore, polarization degree of the polarizing plate and brightness of a screen may be decreased. Further, due to this, contrast ratio (cr) of the liquid crystal display apparatus may be deteriorated. Still further, the common PET film may decrease polarization degree of the polarizer and transmittance of the polarizing plate and make rainbow spots worse, when exposed at high temperature for a long period of time. Moreover, when the PET film is drawn, a portion of, particularly, an end portion of the PET film may suffer from deterioration in optical properties due to its asymmetric molecular orientation in incorporating into a polarizing plate, and thus, there has been a limitation in its use. Further, since the PET film is a drawn film, the film can suffer from rainbow spots in using it in liquid crystal display apparatus.
The background art of the present invention is described in KR 10-2011-0014515 A.